Pub Date : 2024-09-02DOI: 10.1016/j.proci.2024.105561
Antoine Durocher, Luming Fan, Marc Füri, Gilles Bourque, Jeffrey M. Bergthorson, Sean Yun, Patrizio Vena
Micromix fuel injection strategies for hydrogen combustion produce multiple, distributed, compact, and often stratified flames. Single injectors can present highly-tridimensional and non-axisymmetric flame structures along the reactive fuel injection wakes. Their integration into multi-nozzle combustion systems, as commonly found in industrial applications, generates increasingly complex interactions between flames produced through this micromix injection and between neighboring nozzles. Two-dimensional, planar laser-based diagnostics can therefore only provide limited insight into the combustion process of these burners. Five premix/micromix injectors, positioned in a cross pattern, burning pure hydrogen are studied in this work. Three-dimensional (3D) OH volumes are interpolated from 25 OH planar laser-induced fluorescence (PLIF) slices over three inline injectors, resulting in a measurement volume spanning (). The laser diagnostic is registered with the acoustics signal to obtain phase-averaged datasets and capture the complex flame dynamics through a complete period. Comparison with single PLIF measurements demonstrates that, while a single slice provides valuable insight, out-of-plane motion and flame-flame interaction between distributed micromix injections and neighboring nozzles require increasingly complex diagnostics. The reconstruction captures flame merging between micromixed, jet-in-crossflow flames within a single nozzle and between injectors. It highlights the importance of injector clocking to mitigate the formation of hot spots in these systems.
{"title":"Phase-averaged, 3D OH-LIF reconstruction for multi-nozzle, micromixed hydrogen combustion","authors":"Antoine Durocher, Luming Fan, Marc Füri, Gilles Bourque, Jeffrey M. Bergthorson, Sean Yun, Patrizio Vena","doi":"10.1016/j.proci.2024.105561","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105561","url":null,"abstract":"Micromix fuel injection strategies for hydrogen combustion produce multiple, distributed, compact, and often stratified flames. Single injectors can present highly-tridimensional and non-axisymmetric flame structures along the reactive fuel injection wakes. Their integration into multi-nozzle combustion systems, as commonly found in industrial applications, generates increasingly complex interactions between flames produced through this micromix injection and between neighboring nozzles. Two-dimensional, planar laser-based diagnostics can therefore only provide limited insight into the combustion process of these burners. Five premix/micromix injectors, positioned in a cross pattern, burning pure hydrogen are studied in this work. Three-dimensional (3D) OH volumes are interpolated from 25 OH planar laser-induced fluorescence (PLIF) slices over three inline injectors, resulting in a measurement volume spanning (). The laser diagnostic is registered with the acoustics signal to obtain phase-averaged datasets and capture the complex flame dynamics through a complete period. Comparison with single PLIF measurements demonstrates that, while a single slice provides valuable insight, out-of-plane motion and flame-flame interaction between distributed micromix injections and neighboring nozzles require increasingly complex diagnostics. The reconstruction captures flame merging between micromixed, jet-in-crossflow flames within a single nozzle and between injectors. It highlights the importance of injector clocking to mitigate the formation of hot spots in these systems.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-30DOI: 10.1016/j.proci.2024.105682
Rajavasanth Rajasegar, Aleš Srna
Renewably generated synthetic fuels such as poly-oxymethylene ethers (OME) have a significant potential to effectively break the soot-NO trade-off in compression ignition engines by using exhaust gas recirculation (EGR) to maintain low nitrogen oxide (NO) emissions while maintaining good efficiency and simultaneously contributing to circular carbon economy. However, owing to the fundamental differences in properties of OME when compared to fossil-based diesel fuels, it is critical to fully understand its ignition and combustion phenomenology to take advantage of this fuel to its utmost potential. In this context, this work outlines the results of a systematic experimental study performed in a heavy-duty, single-cylinder, optical engine probing the spatial and temporal progression of fuel decomposition and ignition behavior of OME when compared to n-dodecane, a diesel-fuel surrogate. Thermodynamic analysis and optical diagnostics techniques including simultaneous HCHO-PLIF and OH-PLIF complemented by high-speed OH* chemiluminescence were employed along with parametric sweeps of intake temperature and EGR dilution rates. OME does not exhibit any observable low temperature heat release irrespective of the ambient oxygen concentration. Differences in the observed diffusive flame structure such as longer flame lift-off length, less pronounced combustion recession, faster premixed burn at ignition (“volumetric” ignition), non-sooting behavior suggest that the inherent presence of fuel-bound oxygen in OME can skew the air-fuel ratio (AFR) distribution within the jet thereby reducing the reliance of combustion on mixing and air entrainment. This leads to rapid late-cycle oxidation leading to shorter combustion duration and favorable combustion phasing. Results also suggest that OME exhibits relatively weak negative temperature coefficient (NTC) behavior, however, the OME fuel-decomposition kinetic-pathways produce significant concentration of HCHO, which might be erroneously interpreted as a product of cool-flames.
{"title":"Understanding the ignition process and flame structure of conventional and oxygenated fuels under engine relevant conditions – An optical study","authors":"Rajavasanth Rajasegar, Aleš Srna","doi":"10.1016/j.proci.2024.105682","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105682","url":null,"abstract":"Renewably generated synthetic fuels such as poly-oxymethylene ethers (OME) have a significant potential to effectively break the soot-NO trade-off in compression ignition engines by using exhaust gas recirculation (EGR) to maintain low nitrogen oxide (NO) emissions while maintaining good efficiency and simultaneously contributing to circular carbon economy. However, owing to the fundamental differences in properties of OME when compared to fossil-based diesel fuels, it is critical to fully understand its ignition and combustion phenomenology to take advantage of this fuel to its utmost potential. In this context, this work outlines the results of a systematic experimental study performed in a heavy-duty, single-cylinder, optical engine probing the spatial and temporal progression of fuel decomposition and ignition behavior of OME when compared to n-dodecane, a diesel-fuel surrogate. Thermodynamic analysis and optical diagnostics techniques including simultaneous HCHO-PLIF and OH-PLIF complemented by high-speed OH* chemiluminescence were employed along with parametric sweeps of intake temperature and EGR dilution rates. OME does not exhibit any observable low temperature heat release irrespective of the ambient oxygen concentration. Differences in the observed diffusive flame structure such as longer flame lift-off length, less pronounced combustion recession, faster premixed burn at ignition (“volumetric” ignition), non-sooting behavior suggest that the inherent presence of fuel-bound oxygen in OME can skew the air-fuel ratio (AFR) distribution within the jet thereby reducing the reliance of combustion on mixing and air entrainment. This leads to rapid late-cycle oxidation leading to shorter combustion duration and favorable combustion phasing. Results also suggest that OME exhibits relatively weak negative temperature coefficient (NTC) behavior, however, the OME fuel-decomposition kinetic-pathways produce significant concentration of HCHO, which might be erroneously interpreted as a product of cool-flames.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"34 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-30DOI: 10.1016/j.proci.2024.105758
Chen Wang, Jie Ji, Albert Simeoni, Jingbo Xu, Hao Zhang
The leaked liquid fuel has the potential to form a pool fire due to the boundary. The thickness of the fuel () may transition from the millimeter-level to the centimeter-level over time as it leaks. In cases where the pool fires have a at the millimeter-level, it is important not to ignore heat loss from the fuel to the substrate, as this can significantly impact both heat transfer and heat feedback evolution. Experiments were conducted to investigate the heat loss and feedback of n-heptane pool fires with varying and pool diameters (). Results showed that the fuel burning rate remains constant whereas will vary if the flame is in the steady burning stage. As increases, both convection and radiation losses absorbed by the substrate decrease rapidly before decreasing slowly. Smaller values of or larger can result in a greater percentage of heat loss. The effect of heat loss on heat feedback was revealed, and a dominant control mechanism (DCM) for heat feedback was identified for values of ranging from millimeters to centimeters with . As increases, when ≤5.0 mm, DCM transits from convection to radiation; when 5.0∼10.0 mm, DCM transits from radiation to convection, then to radiation; when ≥10.0 mm, DCM transits from conduction to convection, then to radiation again. As increases, when ≤ 5.0 cm, DCM transits from convection to radiation, then to conduction; when continues to increase, DCM is always convection ( = 5.0∼10.0 cm) or transits from convection to radiation ( = 10.0∼20.0 cm). When ≥ 20.0 cm, DCM is always radiation.
{"title":"Experimental study of heat loss and heat feedback of pool fire of millimeter to centimeter fuel thickness","authors":"Chen Wang, Jie Ji, Albert Simeoni, Jingbo Xu, Hao Zhang","doi":"10.1016/j.proci.2024.105758","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105758","url":null,"abstract":"The leaked liquid fuel has the potential to form a pool fire due to the boundary. The thickness of the fuel () may transition from the millimeter-level to the centimeter-level over time as it leaks. In cases where the pool fires have a at the millimeter-level, it is important not to ignore heat loss from the fuel to the substrate, as this can significantly impact both heat transfer and heat feedback evolution. Experiments were conducted to investigate the heat loss and feedback of n-heptane pool fires with varying and pool diameters (). Results showed that the fuel burning rate remains constant whereas will vary if the flame is in the steady burning stage. As increases, both convection and radiation losses absorbed by the substrate decrease rapidly before decreasing slowly. Smaller values of or larger can result in a greater percentage of heat loss. The effect of heat loss on heat feedback was revealed, and a dominant control mechanism (DCM) for heat feedback was identified for values of ranging from millimeters to centimeters with . As increases, when ≤5.0 mm, DCM transits from convection to radiation; when 5.0∼10.0 mm, DCM transits from radiation to convection, then to radiation; when ≥10.0 mm, DCM transits from conduction to convection, then to radiation again. As increases, when ≤ 5.0 cm, DCM transits from convection to radiation, then to conduction; when continues to increase, DCM is always convection ( = 5.0∼10.0 cm) or transits from convection to radiation ( = 10.0∼20.0 cm). When ≥ 20.0 cm, DCM is always radiation.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"84 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180319","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The internal combustion structure of a curved cylindrical rotating detonation combustor (RDC) was experimentally investigated through optical observation and pressure measurements. Experiments were conducted under low back pressure conditions using two combustion chambers having, in both cases, an internal diameter of 17.5 mm, a curvature of radius of 38.1 mm, and an outlet angle of 90 deg, with gaseous CH and O as the propellants. One was made of SUS and the other of resin. In addition to vibrations and bottom center pressure, pressure distribution on the sidewalls was measured for the SUS combustor, and high-speed camera observations of self-luminescence from the radial direction were conducted for the resin combustor. These measurements were compared by varying the equivalence ratio. The frequency analysis results obtained from vibrations and self-luminescence indicated that the strongly-coupled detonation mode exhibited a higher peak frequency, suggesting that the detonation waves may have different propagation speeds or rotational positions. In terms of pressure distribution and self-luminescence, only the strongly-coupled detonation mode inside near the bottom surface exhibited high pressure and brightness values. This suggested the potential for converging pressure by employing rotating detonation waves and a curved tube.
通过光学观测和压力测量，对弯曲圆柱形旋转爆燃燃烧器（RDC）的内部燃烧结构进行了实验研究。实验在低背压条件下进行，使用两个燃烧室，内径均为 17.5 毫米，曲率半径均为 38.1 毫米，出口角均为 90 度，以气态 CH 和 O 作为推进剂。一个由 SUS 制成，另一个由树脂制成。除振动和底部中心压力外，还测量了 SUS 燃烧器侧壁上的压力分布，并对树脂燃烧器进行了径向自发光高速摄像观察。通过改变等效比对这些测量结果进行了比较。振动和自发光的频率分析结果表明，强耦合起爆模式的峰值频率较高，这表明起爆波可能具有不同的传播速度或旋转位置。在压力分布和自发光方面，只有靠近底面的强耦合起爆模式表现出较高的压力和亮度值。这表明，利用旋转爆轰波和弯曲的管子有可能实现压力会聚。
{"title":"Wave-converging pressure increase in curved cylindrical rotating detonation combustors","authors":"Yusuke Oda, Satoru Sawada, Noboru Itouyama, Ken Matsuoka, Jiro Kasahara, Akira Kawasaki, Akiko Matsuo, Ikkoh Funaki","doi":"10.1016/j.proci.2024.105735","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105735","url":null,"abstract":"The internal combustion structure of a curved cylindrical rotating detonation combustor (RDC) was experimentally investigated through optical observation and pressure measurements. Experiments were conducted under low back pressure conditions using two combustion chambers having, in both cases, an internal diameter of 17.5 mm, a curvature of radius of 38.1 mm, and an outlet angle of 90 deg, with gaseous CH and O as the propellants. One was made of SUS and the other of resin. In addition to vibrations and bottom center pressure, pressure distribution on the sidewalls was measured for the SUS combustor, and high-speed camera observations of self-luminescence from the radial direction were conducted for the resin combustor. These measurements were compared by varying the equivalence ratio. The frequency analysis results obtained from vibrations and self-luminescence indicated that the strongly-coupled detonation mode exhibited a higher peak frequency, suggesting that the detonation waves may have different propagation speeds or rotational positions. In terms of pressure distribution and self-luminescence, only the strongly-coupled detonation mode inside near the bottom surface exhibited high pressure and brightness values. This suggested the potential for converging pressure by employing rotating detonation waves and a curved tube.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"111 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-30DOI: 10.1016/j.proci.2024.105302
Shoya Yasunaga, Shinji Nakaya, Mitsuhiro Tsue
The present study investigates the effects of fuel penetration height on combustion instabilities in an ethylene-fueled scramjet model combustor with a cavity flameholder. Experiments were performed at the stagnation temperature of 1900 K, the stagnation pressure of 0.37 MPa, and the Mach number of 2. Three fuel injection orifice diameters:2.3, 2.4, and 2.5 mm, were tested to elucidate the effects of ethylene penetration height on combustion instabilities. Furthermore, high-speed measurements of CH* chemiluminescence and shadowgraphs were performed with high-speed video cameras. To examine the dynamics of the combustion instabilities, time-resolved CH* chemiluminescence images and shock parameters, extracted from snapshots of shadowgraphs, were analyzed using a non-linear dimensionality reduction algorithm: Gaussian Process Dynamical Model (GPDM). Thereafter, further analyses on the acquired latent variables were conducted with Recurrence Plot (RP). The experimental results showed that the fuel equivalence ratio (ϕ) range for cavity shear-layer combustion mode expanded as d decreased. Furthermore, for ϕ = 0.18, the instability behavior remarkably changed at around = 2.4 mm. Therefore, the instability dynamics for ϕ = 0.18 were investigated using GPDM and RP including results from our previous study ( = 2, 3, and 4 mm), revealing differences in the instability behaviors. For = 3 and 4 mm, jet-wake combustion and ram combustion modes were established alternately with a frequency of about 1600 Hz. In contrast, at = 2.4 and 2.5 mm, although a similar instability in the = 4 mm case was present at almost the same oscillation frequency, a different instability behavior was also confirmed. This additional instability exhibited an intermediate state between jet-wake combustion and ram combustion modes. These two instabilities emerged aperiodically. For an unstable combustion in shear layer observed for = 2 and 2.3 mm, corresponding RPs exhibited black patches, indicating that the oscillation amplitude diminished substantially.
{"title":"Combustion instability analysis in an ethylene-fueled scramjet combustor under various fuel penetration height conditions using an image-based nonlinear dimensionality reduction method","authors":"Shoya Yasunaga, Shinji Nakaya, Mitsuhiro Tsue","doi":"10.1016/j.proci.2024.105302","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105302","url":null,"abstract":"The present study investigates the effects of fuel penetration height on combustion instabilities in an ethylene-fueled scramjet model combustor with a cavity flameholder. Experiments were performed at the stagnation temperature of 1900 K, the stagnation pressure of 0.37 MPa, and the Mach number of 2. Three fuel injection orifice diameters:2.3, 2.4, and 2.5 mm, were tested to elucidate the effects of ethylene penetration height on combustion instabilities. Furthermore, high-speed measurements of CH* chemiluminescence and shadowgraphs were performed with high-speed video cameras. To examine the dynamics of the combustion instabilities, time-resolved CH* chemiluminescence images and shock parameters, extracted from snapshots of shadowgraphs, were analyzed using a non-linear dimensionality reduction algorithm: Gaussian Process Dynamical Model (GPDM). Thereafter, further analyses on the acquired latent variables were conducted with Recurrence Plot (RP). The experimental results showed that the fuel equivalence ratio (ϕ) range for cavity shear-layer combustion mode expanded as d decreased. Furthermore, for ϕ = 0.18, the instability behavior remarkably changed at around = 2.4 mm. Therefore, the instability dynamics for ϕ = 0.18 were investigated using GPDM and RP including results from our previous study ( = 2, 3, and 4 mm), revealing differences in the instability behaviors. For = 3 and 4 mm, jet-wake combustion and ram combustion modes were established alternately with a frequency of about 1600 Hz. In contrast, at = 2.4 and 2.5 mm, although a similar instability in the = 4 mm case was present at almost the same oscillation frequency, a different instability behavior was also confirmed. This additional instability exhibited an intermediate state between jet-wake combustion and ram combustion modes. These two instabilities emerged aperiodically. For an unstable combustion in shear layer observed for = 2 and 2.3 mm, corresponding RPs exhibited black patches, indicating that the oscillation amplitude diminished substantially.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"11 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-30DOI: 10.1016/j.proci.2024.105752
Hao-Yu Hsieh, Seyed Morteza Mousavi, Andrei N. Lipatnikov, Shenqyang (Steven) Shy
To experimentally explore the influence of Lewis number , laminar flame thickness , pressure , and unburned gas temperature on turbulent flame speed , a set of conditions is designed by adjusting nitrogen mole fraction in lean H/O/N () and stoichiometric CH/O/N () mixtures. The adjustment is performed by simulating complex-chemistry laminar flames to obtain the same laminar flame speeds not only for different fuels, but also for different pressures (1, 2, and 5 atm). The mixtures are characterized by significantly different at K and 400 K, whereas variations in with the temperature are sufficiently weak. Moreover, laminar flame thicknesses are approximately equal for H-based and CH-based mixtures at the same , but are significantly decreased with increasing pressure. For this set of conditions, is measured by applying schlieren imaging techniques to film expansion of centrally ignited, statistically spherical flames in homogeneous isotropic turbulence generated by a dual-chamber, constant-pressure, fan-stirred explosion facility. Analyses of the measured data show the following trends. First, turbulent flame speed is increased by both and , whereas is decreased with increasing . Second, turbulent flame speed measured at different and can be predicted by allowing for and . Thus, the present data do not call for explicitly substituting normalized pressure or temperature into a turbulent flame speed approximation. Third, is increased with decreasing laminar flame thickness. Fourth, speeds of the lean H/O/N flames are higher when compared to the stoichiometric CH/O/N flames, with this difference is increased (reduced) by (, respectively). Fifth, all measured data on can quantitatively be described by substituting and with the counterpart characteristics of highly strained twin laminar flames. The latter finding supports leading point concept of premixed turbulent combustion.
{"title":"Experimental study of the influence of Lewis number, laminar flame thickness, temperature, and pressure on turbulent flame speed using hydrogen and methane fuels","authors":"Hao-Yu Hsieh, Seyed Morteza Mousavi, Andrei N. Lipatnikov, Shenqyang (Steven) Shy","doi":"10.1016/j.proci.2024.105752","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105752","url":null,"abstract":"To experimentally explore the influence of Lewis number , laminar flame thickness , pressure , and unburned gas temperature on turbulent flame speed , a set of conditions is designed by adjusting nitrogen mole fraction in lean H/O/N () and stoichiometric CH/O/N () mixtures. The adjustment is performed by simulating complex-chemistry laminar flames to obtain the same laminar flame speeds not only for different fuels, but also for different pressures (1, 2, and 5 atm). The mixtures are characterized by significantly different at K and 400 K, whereas variations in with the temperature are sufficiently weak. Moreover, laminar flame thicknesses are approximately equal for H-based and CH-based mixtures at the same , but are significantly decreased with increasing pressure. For this set of conditions, is measured by applying schlieren imaging techniques to film expansion of centrally ignited, statistically spherical flames in homogeneous isotropic turbulence generated by a dual-chamber, constant-pressure, fan-stirred explosion facility. Analyses of the measured data show the following trends. First, turbulent flame speed is increased by both and , whereas is decreased with increasing . Second, turbulent flame speed measured at different and can be predicted by allowing for and . Thus, the present data do not call for explicitly substituting normalized pressure or temperature into a turbulent flame speed approximation. Third, is increased with decreasing laminar flame thickness. Fourth, speeds of the lean H/O/N flames are higher when compared to the stoichiometric CH/O/N flames, with this difference is increased (reduced) by (, respectively). Fifth, all measured data on can quantitatively be described by substituting and with the counterpart characteristics of highly strained twin laminar flames. The latter finding supports leading point concept of premixed turbulent combustion.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"31 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180321","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The mechanism of flame stabilisation using nanosecond repetitively pulsed (NRP) plasma discharges in a turbulent, premixed methane–air flame at high velocities was investigated, focusing on the lean extinction limits. In contrast to the majority of the existing studies that considered NRP discharges as an assistance to conventional stabilisers, here, no other flame-holding method is used. High-speed (10 kHz) OH* chemiluminescence showed that the plasma discharges produce individual OH*-pockets that merge together at a high enough frequency to form a continuous flame sheet. Increasing the discharge repetition frequency from 5 kHz to 10 kHz improves flame stability, but no change in flame structure and stability was observed when the frequency was increased beyond 10 kHz. Change in the plasma energy level in the range studied had little effect on the flame structure. The lean extinction limit was quantified at various flow velocities, equivalence ratios, discharge frequencies and energy levels. It was observed that the trend of the extinction equivalence ratio with bulk velocity was similar to that of a conventional bluff body stabilised flame and that plasma-only stabilised flame was equally effective at certain operating conditions. An effort to correlate the stabilisation limits by a conventional Damköhler number Da was made but was not satisfactory due to the presence of a characteristic flameholder lengthscale present in the Da expression. A modified Da was proposed to take the spark frequency effects into account, but this was not successful either. In contrast, the spread of the extinction data was smaller when a critical Karlovitz number was used, hence offering a way to extrapolate the present data to other conditions. The experiments demonstrate that NRP discharges can be used as an alternative stabilisation method for high-speed turbulent premixed flames.
{"title":"Stabilisation limits of turbulent premixed flames by nanosecond repetitively pulsed discharges","authors":"Rohit Singh Pathania, Preethi Rajendram Soundararajan, Epaminondas Mastorakos","doi":"10.1016/j.proci.2024.105722","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105722","url":null,"abstract":"The mechanism of flame stabilisation using nanosecond repetitively pulsed (NRP) plasma discharges in a turbulent, premixed methane–air flame at high velocities was investigated, focusing on the lean extinction limits. In contrast to the majority of the existing studies that considered NRP discharges as an assistance to conventional stabilisers, here, no other flame-holding method is used. High-speed (10 kHz) OH* chemiluminescence showed that the plasma discharges produce individual OH*-pockets that merge together at a high enough frequency to form a continuous flame sheet. Increasing the discharge repetition frequency from 5 kHz to 10 kHz improves flame stability, but no change in flame structure and stability was observed when the frequency was increased beyond 10 kHz. Change in the plasma energy level in the range studied had little effect on the flame structure. The lean extinction limit was quantified at various flow velocities, equivalence ratios, discharge frequencies and energy levels. It was observed that the trend of the extinction equivalence ratio with bulk velocity was similar to that of a conventional bluff body stabilised flame and that plasma-only stabilised flame was equally effective at certain operating conditions. An effort to correlate the stabilisation limits by a conventional Damköhler number Da was made but was not satisfactory due to the presence of a characteristic flameholder lengthscale present in the Da expression. A modified Da was proposed to take the spark frequency effects into account, but this was not successful either. In contrast, the spread of the extinction data was smaller when a critical Karlovitz number was used, hence offering a way to extrapolate the present data to other conditions. The experiments demonstrate that NRP discharges can be used as an alternative stabilisation method for high-speed turbulent premixed flames.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-29DOI: 10.1016/j.proci.2024.105712
Carlos Chiquete, Mark Short
The stability and propagation characteristics of gaseous detonations are numerically investigated, specifically in configurations where global front surface curvature plays a significant role. The simulations use idealized constitutive models representing a weakly unstable mixture and the simulated geometries include both two-dimensional arc and spherical shell sections with rigid walls and a straight channel geometry with compliant confinement. Depending on the inner and outer arc radius, differing levels of curvature can be imparted on the propagating wave in the two curved geometries. For thinner explosive regions, cellular type instabilities develop as the wave propagates around the arc and shell. However, as the thickness of the explosive increases and progressively greater surface curvature is imposed, laminar flow regions develop which can coexist with regions dominated by unstable cellular propagation. Here, the appearance and persistence of this laminar zone is shown to coincide with a critical level of surface curvature for both the arc and shell geometries. This critical curvature concept is also tested in the corresponding straight channel configuration with a compliant confiner, which similarly produces global surface curvature on the propagating detonation front but now as function of imposed wall divergence. Similarly, the propagation in the channel is found to stabilize when the maximum surface curvature exceeds a certain critical value that is close to the analog from the curved geometries. These results support the likely existence of a critical surface curvature mechanism or criterion that ensures the stabilization of a nominally unstable cellular detonation.
{"title":"Curvature effect on stabilization of cellular detonations in channel, circular arc and spherical shell geometries","authors":"Carlos Chiquete, Mark Short","doi":"10.1016/j.proci.2024.105712","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105712","url":null,"abstract":"The stability and propagation characteristics of gaseous detonations are numerically investigated, specifically in configurations where global front surface curvature plays a significant role. The simulations use idealized constitutive models representing a weakly unstable mixture and the simulated geometries include both two-dimensional arc and spherical shell sections with rigid walls and a straight channel geometry with compliant confinement. Depending on the inner and outer arc radius, differing levels of curvature can be imparted on the propagating wave in the two curved geometries. For thinner explosive regions, cellular type instabilities develop as the wave propagates around the arc and shell. However, as the thickness of the explosive increases and progressively greater surface curvature is imposed, laminar flow regions develop which can coexist with regions dominated by unstable cellular propagation. Here, the appearance and persistence of this laminar zone is shown to coincide with a critical level of surface curvature for both the arc and shell geometries. This critical curvature concept is also tested in the corresponding straight channel configuration with a compliant confiner, which similarly produces global surface curvature on the propagating detonation front but now as function of imposed wall divergence. Similarly, the propagation in the channel is found to stabilize when the maximum surface curvature exceeds a certain critical value that is close to the analog from the curved geometries. These results support the likely existence of a critical surface curvature mechanism or criterion that ensures the stabilization of a nominally unstable cellular detonation.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"113 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-29DOI: 10.1016/j.proci.2024.105756
Sriram Bharath Hariharan, Paul M. Anderson, Yejun Wang, Waruna D. Kulatilaka, Michael J. Gollner, Elaine S. Oran
The blue whirl is a conical, near-limit flame with a bright, blue ring, occurring at low heat-release rates that can stabilize over a pool of liquid fuel. This unique structure forms following suppression of soot formation in a laminar fire whirl under the influence of vortex breakdown. Recent literature on the blue whirl has hypothesized and predicted the existence of a triple flame at the blue ring. In this work, we explore the distribution of various chemical species in the flame to quantitatively establish a map of equivalence ratio around the flame. Using high-speed chemiluminescence and planar laser-induced fluorescence, the distribution of OH, PAH and CH radicals were measured. The OH*/CH* ratio was used to estimate the local equivalence ratio. Results show that the blue ring is mostly stoichiometric, but there is a small rich region below it, towards the fuel layer, and a lean region above it, towards the wake of the vortex breakdown bubble. This structure provides experimental evidence that a triple flame exists in the blue whirl. The time scales of flow within the recirculation zone are estimated using soot traces that are observed occasionally, and then used to estimate a range of Damköhler numbers that can lead to stable blue whirl formation, providing an important scaling factor to design clean, practical burners using the blue whirl regime.
{"title":"The chemical structure of triple flames in laminar blue whirls","authors":"Sriram Bharath Hariharan, Paul M. Anderson, Yejun Wang, Waruna D. Kulatilaka, Michael J. Gollner, Elaine S. Oran","doi":"10.1016/j.proci.2024.105756","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105756","url":null,"abstract":"The blue whirl is a conical, near-limit flame with a bright, blue ring, occurring at low heat-release rates that can stabilize over a pool of liquid fuel. This unique structure forms following suppression of soot formation in a laminar fire whirl under the influence of vortex breakdown. Recent literature on the blue whirl has hypothesized and predicted the existence of a triple flame at the blue ring. In this work, we explore the distribution of various chemical species in the flame to quantitatively establish a map of equivalence ratio around the flame. Using high-speed chemiluminescence and planar laser-induced fluorescence, the distribution of OH, PAH and CH radicals were measured. The OH*/CH* ratio was used to estimate the local equivalence ratio. Results show that the blue ring is mostly stoichiometric, but there is a small rich region below it, towards the fuel layer, and a lean region above it, towards the wake of the vortex breakdown bubble. This structure provides experimental evidence that a triple flame exists in the blue whirl. The time scales of flow within the recirculation zone are estimated using soot traces that are observed occasionally, and then used to estimate a range of Damköhler numbers that can lead to stable blue whirl formation, providing an important scaling factor to design clean, practical burners using the blue whirl regime.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"31 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-29DOI: 10.1016/j.proci.2024.105745
Rajat Sawanni, Ömer L. Gülder
A parametric study using ethylene as fuel was undertaken which examines the efficacy of concentration based and soot production rate (SPR) based parameters for assessing the pressure scaling of sooting processes in a counterflow diffusion flame. Two experimental designs pertaining to constant flow residence times (Case A), and constant carbon mass flux (Case B) were respectively implemented for pressures between 1 to 6 bars and across peak temperatures ranging from K for , K for , and K for flames. A diffuse line-of-sight based extinction imaging diagnostic was employed for the measurement of soot concentrations. The evaluation of SPR follow a transport based coupling of inferred gaseous precursors, temperatures and velocity fields from detailed 1D OpenSMOKE++ simulations and soot concentrations from extinction measurements. The use of concentration based parameters, namely peak () and integrated soot volume fractions (), is noted to be dependent on the Case A or B with little information discernible about the pressure effects in an experimental setting. The use of production rate based parameters, namely mean SPR () removes the disparity of pressure scaling exponents across cases A and B but inherits the dependency to peak flame temperature, and gaseous precursor concentrations. An empirical fit of local SPR to acetylene and pyrene concentrations reveals a universal Arrhenius activation energy parameter in the high-temperature region (1300–2000 K) of the studied flames. The global activation energy is noted to remain roughly constant across varying peak flame temperatures, fuel flux, flow residence times and pressure. Consequently, we propose a soot yield parameter (), calculated as the mean soot production rate normalized to acetylene and pyrene mass fractions which is noted to universally scale with pressure as .
以乙烯为燃料进行了一项参数研究，考察了基于浓度和烟尘产生率（SPR）的参数在评估逆流扩散火焰中烟尘过程的压力缩放方面的功效。分别针对 1 至 6 巴的压力和 K、K 和 K 的火焰峰值温度，采用了恒定流动停留时间（情况 A）和恒定碳质量流量（情况 B）的两种实验设计。采用基于扩散视线的消光成像诊断来测量烟尘浓度。在对 SPR 进行评估时，采用了基于传输的耦合方法，将从详细的 1D OpenSMOKE++ 模拟中推断出的气体前体、温度和速度场与从消光测量中得到的烟尘浓度结合起来。使用基于浓度的参数，即峰值（）和综合烟尘体积分数（），需要注意的是，这些参数取决于情况 A 或情况 B，在实验环境中几乎无法辨别有关压力影响的信息。使用基于生产率的参数，即平均 SPR（），消除了 A 和 B 两种情况下压力缩放指数的差异，但继承了对火焰峰值温度和气体前体浓度的依赖性。局部 SPR 与乙炔和芘浓度的经验拟合显示，在所研究火焰的高温区（1300-2000 K）存在一个通用的阿伦尼乌斯活化能参数。我们注意到，在不同的火焰峰值温度、燃料流量、流动停留时间和压力条件下，总活化能基本保持不变。因此，我们提出了一个烟尘产生率参数（），计算方法是将平均烟尘产生率归一化为乙炔和芘的质量分数。
{"title":"A tractable methodology for assessing the pressure scaling of sooting processes in a counterflow diffusion flame from 1 to 6 bar","authors":"Rajat Sawanni, Ömer L. Gülder","doi":"10.1016/j.proci.2024.105745","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105745","url":null,"abstract":"A parametric study using ethylene as fuel was undertaken which examines the efficacy of concentration based and soot production rate (SPR) based parameters for assessing the pressure scaling of sooting processes in a counterflow diffusion flame. Two experimental designs pertaining to constant flow residence times (Case A), and constant carbon mass flux (Case B) were respectively implemented for pressures between 1 to 6 bars and across peak temperatures ranging from K for , K for , and K for flames. A diffuse line-of-sight based extinction imaging diagnostic was employed for the measurement of soot concentrations. The evaluation of SPR follow a transport based coupling of inferred gaseous precursors, temperatures and velocity fields from detailed 1D OpenSMOKE++ simulations and soot concentrations from extinction measurements. The use of concentration based parameters, namely peak () and integrated soot volume fractions (), is noted to be dependent on the Case A or B with little information discernible about the pressure effects in an experimental setting. The use of production rate based parameters, namely mean SPR () removes the disparity of pressure scaling exponents across cases A and B but inherits the dependency to peak flame temperature, and gaseous precursor concentrations. An empirical fit of local SPR to acetylene and pyrene concentrations reveals a universal Arrhenius activation energy parameter in the high-temperature region (1300–2000 K) of the studied flames. The global activation energy is noted to remain roughly constant across varying peak flame temperatures, fuel flux, flow residence times and pressure. Consequently, we propose a soot yield parameter (), calculated as the mean soot production rate normalized to acetylene and pyrene mass fractions which is noted to universally scale with pressure as .","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"10 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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